Petroleum pitch competes with coal tar pitch in many applications where the pitch is used as a carbon source and/or as a binder. The critical properties that are evaluated when deciding what type of pitch to use include: (a) flow properties, as measured by softening point and/or viscosity, and (b) carbon yield, as measured by ASTM D 2488, Coking Value by Modified Conradson Carbon.
Another pitch property that is also becoming of increasing interest is the polycyclic aromatic hydrocarbon (PAH) content. The U.S. Pat. No. 5,746,906 patent describes a coal tar pitch having a low polycyclic aromatic hydrocarbon content and a method of making such pitch where a high softening point coal tar pitch (softening point of 120–175° C.) was mixed with a low softening point petroleum pitch to make a binder pitch having a softening point of 107–114° C. and a PAH content slightly above 15,000 ppm.
In the manufacture of coal tar pitch, if more low boiling point materials are left in the pitch product, the resulting product has a lower softening point and a lower viscosity. In the case of petroleum pitch manufacturing, a high softening point petroleum bitch can be “cut back” with a hydrocarbon liquid material to produce a petroleum pitch having a lower softening point and a lower viscosity at a given temperature. It has long been understood in the industry, until the present invention, that this relationship between the softening point and viscosity was unchangeable (i.e., if one were lowered, the other would be lowered also).
Generally speaking, for a given softening point/viscosity, a petroleum pitch will have a lower carbon yield than a coal tar pitch. However, despite a potentially lower carbon yield, petroleum pitch offers certain advantages over coal tar pitch. One advantage that petroleum pitch has over coal tar pitch is the increased solids content of the petroleum pitch material. Therefore, it is desired in the industry to fine a way to improve the other critical property (i.e., the “flow” or viscosity) of petroleum pitch.
In the past, many types of materials have been used to modify the flow properties of such petroleum products as pitch and asphalt. Historically, these have been petroleum based, non-oxygenated hydrocarbons such as diesel fuel or various types of fuel oils, kerosene or various cutback oils. However, the use of these solvent “cutback” materials often causes problems with flash point and volatility if too much solvent is used.
Examples of viscosity modification of bituminous materials include the use of a fluoro or chlorofluoro derivative of lower alkanes, such as disclosed in Smith et al., U.S. Pat. No. 4,151,003.
Still other methods include reducing the viscosity of heavy hydrocarbon oils by preheating a stream of heavy carbon hydrocarbon oil in a stream of gas, mixing under pressure, and passing through a nozzle to form fine oil droplets such that a strong shearing action is created as the heavy oil and gas are forced through an orifice, as described in Dawson et al. U.S. Pat. No. 5,096,566.
Various other viscosity modified emulsions are also described. For example, the Schilling U.S. Pat. No. 5,320,671 describes mixing a bituminous emulsion aggregate slurry with a cationic emulsifier prepared as a reaction process of a polyamine with polycarboxylic acid hydrides and a kraft lignin. Other emulsions are described in the Schilling U.S. Pat. No. 5,328,505, Holleran, U.S. Pat. No. 5,474,607, and Krivohlavek, U.S. Pat. No. 5,834,359.
Still other dispersant/emulsions are described in Wallace, U.S. Pat. No. 2,686,728; Ljusberg-Wahren, U.S. Pat. No. 4,957,511; McDonald, U.S. Pat. No. 4,085,078; Haire et al., U.S. Pat. No. 4,877,513 (also generally described in the abstract Haire, B. UNITAR 5th International Conference (Caracas 8/4-9/91) Proceedings V2, 121–126 (1991)); and Ohzeki et al., U.S. Pat. No. 4,539,012.
Another viscosity modifier is dibasic ester (DBE) which is a solvent that is used for certain coal tar pitch and tars that are pourable at room temperature. However, the dibasic esters are expensive and are limited in their applicability to less viscous coal tars. Also, the dibasic esters do not adequately modify the viscosity of more viscous pitches such as petroleum pitches.
Therefore, there is a need to produce a viscosity modifier that is useful with pitches, and in particular, petroleum pitches, but does not have the above described drawbacks associated with the viscosity modifiers currently in use.
In particular, there is a need for a viscosity modifier that provides improved characteristics to the pitch and the pitch end product.
There is a further need for a viscosity modifier useful with heavy hydrocarbons that provide improved safety features such as low volatility and low toxicity.
In the past, ethylene glycol has been used as a lubricant for coal tar pitches. U.S. Pat. No. 2,686,728 taught mixing 98 parts pulverized coal tar pitch with 2 parts, by, weight, of diethylene glycol and 5 parts, by with, water. The water helped to distribute the glycol over the pitch particles. Until the present invention, however, no one had thought to use dihydric alcohols such as ethylene glycol as a viscosity reduction agent for pitches, and, in particular, petroleum pitch.